Automobile exhaust gas and industrial exhaust gases produced by the evaporation of organic solvents during the drying process in the paint industry, for example, have become an environmental problem. There is thus a need for efficient recovery of such organic gases.
Gasoline, which is the fuel used in automobiles, is highly volatile. Therefore, when the automobile is moving or is parked under the scorching sun, gasoline vaporizes in the fuel tank, and the gasoline vapor is discharged into the atmosphere. Gasoline vapor is also produced during refueling.
Accordingly, to prevent gasoline vapor from being discharged from the automobile, a canister is provided in the automobile and active carbon or the like contained in the canister is used as an absorbent material. For example, JP Patent Publication (Kokai) No. 2005-35812 A describes that by allowing an organic substance to be adsorbed on starting active carbon having a wide range of pore sizes so that the smaller-sized pores are selectively blocked, the resulting active carbon has excellent adsorption/desorption properties. Patent Document 1 also describes that a canister using such active carbon suppresses the adsorbed component from leaking.
However, porous materials having pores such as active carbon for the adsorption and removal of organic gases have been developed and are in use. The adsorption mechanism of such organic gases is reported to be that the organic gas is liquefied under high pressure inside micropores of the porous material and is retained by adsorption inside the micropores.
Accordingly, the pore size of the adsorbent material is optimized according to the molecular weight, concentration and the like of the organic gas to be adsorbed. For adsorption of comparatively low-molecular-weight organic gases, such as butane, a porous material having a large number of micropores with a diameter of 5 nm or less is optimal. In contrast, for a porous material having large pores of a diameter of 10 nm or more, it is difficult for the organic gas to be liquefied under high pressure inside the pores, so that the low-molecular-weight gas is not retained by adsorption.